In U.S. Pat. No. 3,708,296 to Sheldon I. Schlesinger entitled "Photopolymerization of Epoxy Monomers" issued Jan. 2, 1973, there are disclosed novel compositions comprising various epoxide materials and certain latent curing catalysts therefor. Such compositions are photosensitive and when exposed to an energy source such as actinic radiation yield epoxy polymers which are receptive to ink and possess inherent toughness, abrasion resistance, adherence to metal surfaces, resistance to chemical attack, etc. and are thus valuable for many applications particularly those involving formation of acid and alkali resist images for chemical milling, gravure images, offset plates, stencil-making, etc.
Additionally, in copending application Ser. No. 297,829 filed Oct. 16, 1972, now abandoned, and commonly assigned herewith, certain copolymers of glycidyl methacrylate and allyl glycidyl ether were found to exhibit improved curing rates, electron sensitivity, photosensitivity and other properties which rendered them especially suitable for use in preparation of articles for storing and recording information from laser or electron beam sources or in microfilm preparation, in the presence of the sensitizers therein described.
It has now been discovered that specific epoxide materials, copolymers of glycidyl acrylate and allyl glycidyl ether, specially prepared, when utilized with latent curing catalysts, are unique in being tacky at an elevated temperature before light curing and becoming hard and non-tacky upon exposure to light in an imagewise manner. The copolymers also have the property of being substantially non-tacky at room temperature and have the ability to imbibe toner or pigment in inverse proportion to the amount of light received. Such properties render the copolymers eminently suitable for use in dry photopolymer imaging processes, i.e. imaging processes which permit elimination of solvents. The ecological advantage of such a process which is devoid of waste-solvent disposal is readily evident.
Various systems have been heretofore described in which a tacky photopolymer is exposed imagewise to actinic radiation whereby the exposed areas are crosslinked or polymerized losing their tack after which a dye, pigment or toner is applied to the surface. Only the unexposed areas pick up the colorant because of their tack thus forming a positive reproduction of the image.
Such processes have been used to transfer images from the original and are known commercially as Adherography or Custom Toning. However, none of the existing systems are without attendant disadvantages. The use of a system that is tacky at room temperature requires special handling of the unexposed film and fixing of the image after development. Conversely, with systems that are non-tacky at room temperature, solvents and other liquids are often necessary to make the substances tacky when tackiness is required. Many of the systems have poor shelf life and require long exposure times or high energy requirements, etc. The majority of such prior systems involve addition-polymerization reaction mechanisms which have the disadvantageous tendency of absorbing oxygen from the air which acts as a polymerization inhibitor, lowers the radiation-sensitivity of the system and necessitates, in addition to high intensity sources of radiation, covering the photopolymer surface with a plastic film to protect the tacky coating and to prevent oxygen inhibition.
There is therefore a continued need in the art for dry photopolymer imaging systems which are devoid of the disadvantages enumerated above.